This invention relates to a hydraulic drilling machine, especially a rock drill comprising a striking apparatus, a rotating motor and a feed motor, as well as pumps and valves necessary for their operation and control.
French Pat. No 2,129,276 discloses a hydraulic drilling machine in which the striking apparatus is connected in series with the rotating motor of the drill, whereby increasing rotation resistance and pressure drop across the rotating motor decreases the power of the striking apparatus in order to avoid jamming of the drill steel. When starting to drill, as well as when drilling considerably nonhomogenous material, the function of this arrangement, however, does not serve the purpose. When the drill is rotating freely, or in a soft material, the striking force is at its maximum even if the striking and feed forces ought to be small in order to feed the drill slowly into contact with a hard material.
In a drilling machine according to U.S. Pat. No. 3,979,944, this disadvantage has been eliminated by means of a suitable valve control. When using conventional valves it is not possible to accomplish a stepless control at reasonable cost.
A principal object of this invention is to provide an improved drilling machine in which the rotating, striking and feed forces are automatically and steplessly adjusted in proportion to the nature of the material to be drilled so that boring of the hole proceeds without difficulty even on an oblique and uneven rock surface, and also so that when drilling is fissured rock the drill steel does not jam, but the drilling can continue in difficult and changing circumstances.
In order to realize this object, for example the feed force, when starting to drill into an oblique wall, has to be considerably smaller than in normal drilling. The adjustability of the feed force in proportion to individual starting situations offers advantages in changeable starting conditions. When drilling into a fissure, the need for automatic control of the feed force is great. The feed force must be small enough in order to prevent the drill steel from wedging deeper into a fissure. When the drill steel is badly jammed, the feed force must change its direction in order to pull the drill out of the hole. Thereby it is also advantageous to decrease the striking force. When the drill has been freed, a new effort to penetrate through the fissure can be started.